Coil loads images at initial resolution, causing rescaling to look pixelated

[Martmists-GH]

Describe the bug

The image is downscaled when shown at a low resolution, however when the Density increases, the image does not rescale appropriately.
(open images in new tab for better example)

To Reproduce

var scale by remember { mutableStateOf(1f) }  // Add a way to change this
val oldDensity = LocalDensity.current
val newDensity = Density(oldDensity.density * scale, oldDensity.fontScale)
CompositionLocalProvider(
    LocalDensity provides newDensity
) {
    AsyncImage(url, "")
}

Version
Coil 3.3.0, both on desktop and web (wasm)

[colinrtwhite]

This is expected behaviour AsyncImage won't automatically restart the request when the density changes. It's the same case when the window is resized and the size of the AsyncImage changes. You'll have to manually restart the request by changing one of the parameters of the ImageRequest.

[Martmists-GH]

What parameter could I change? Am I expected to switch between alpha 1f and 0.999999f every time using a LaunchedEffect?

I attempted .memoryCacheKey(LocalDensity.current.density.toString()) but that re-fetches the URL every time the density changes and causes the previous version of the image to disappear until loaded.

[colinrtwhite]

Yep, you're right there isn't a great way to restart a request with AsyncImage at the moment. It was possible to use the Parameters API in Coil 2.x, but that was replaced by Extras in 3.x. There's an efficient restart method on AsyncImagePainter, but there's no way to access the underlying AsyncImagePainter used by AsyncImage. I think we could probably add a way to expose the underlying AsyncImagePainter.

For now your best bet would be to use rememberAsyncImagePainter with rememberConstraintsSizeResolver like in this example. That'll expose the AsyncImagePainter.restart method while still automatically subsampling the image to fix the target.

I'll work on improving this hopefully for the next release.